The Food and Drug Administration says preliminary results from a study of 5,000 patients taking the drug suggests an increased risk of heart problems and stroke. The drug's manufacturer Genentech, a unit of Swiss pharmaceutical giant Roche, designed the study to track the long-term safety of the drug over five years.

A representative for Genentech says final results are not expected until 2012. The South San Francisco-based company says it will continue gathering safety information about Xolair.

The results of recent trials that tested much-anticipated Alzheimer's disease drugs dashed the hopes of patients with the debilitating condition. The most recent disappointment came from the large trial for solanezumab, by Eli Lilly, announced last month.